Saint Elmo's fire

Saint Elmo's fire

noun usually abbreviated to: St Elmo's fire

(not in technical usage) a luminous region that sometimes appears around church spires, the masts of ships, etc. It is a corona discharge in the air caused by atmospheric electricityAlso called: corposant

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Word Origin

C16: so called because it was associated with Saint Elmo (a corruption, via Sant'Ermo, of Saint Erasmus, died 303) the patron saint of Mediterranean sailors

Saint Elmo's fire

[sānt ĕl′mōz]

A visible and sometimes audible electric discharge projecting from a pointed object, such as the mast of a ship or the wing of an airplane, during an electrical storm. First identified as an electrical phenomenon by Benjamin Franklin in 1749, St. Elmo's fire is a bluish-white plasma caused by the release of electrons in a strong electric field (200 or more volts per cm); the electrons have enough energy to ionize atoms in the air and cause them to glow. The phenomenon appears near pointed objects because electrical fields generated by charged surfaces are strongest where curves are sharpest. It is named after St. Elmo, the patron saint of mariners, as the phenomenon was often observed by sailors during thunderstorms at sea. See also lightning rod.